In forming machines having one or more forming stations, a section sheared off from a bar is often fed to the first forming station for forming. The bar is normally sheared in a separate shearing station by means of a fixed blade and a shearing blade which is displaceable relative thereto and is moved back and forth by a shearing slide. It is known to design the fixed blade and the shearing blade in various possible ways.
In cold-forming machines, for example, closed circular blades are often used as the fixed blade and the shearing blade. The bar to be sheared is pushed into passages through the fixed blade and the shearing blade, and the shearing blade is then rapidly displaced transversely to the bar, as a result of which a section is sheared off from the bar.
In hot-forming machines, the fixed blade and the shearing blade are normally designed as half blades, that is to say as blades which bear against the bar only over part of the bar circumference, the bar to be sheared being held between the half blades and clamping jaws during the shearing. After the shearing, the clamping jaws are moved away for the advance and aeration of the bar. To center the bar, a separate centering device is provided.
Disclosed in WO 01/28711 A1 is a forming machine having a shearing device which has a slotted circular blade, consisting of a fixed blade designed as a half blade and of a centering and clamping piece movable relative thereto, and a shearing blade which interacts with the slotted circular blade and is displaceable relative thereto and is designed as a closed circular blade.
EP 0 011 293 A discloses a forming machine having a shearing device, the shearing part of which has two shearing blades, a first shearing blade, during forward movements of the shearing part, shearing bar sections which are fed to a first forming station, and a second shearing blade, during backward movements of the shearing part, shearing bar sections which are fed to a second forming station.
With all these known shearing devices, scrap pieces are sheared at a bar transition from a preceding bar to be sheared to the following bar to be sheared, these scrap pieces comprising at least the end of the preceding bar and the start of the following bar. Since these scrap pieces do not have the desired length of bar sections to be subsequently processed in the following forming stations, they are normally rejected and are not fed to the forming stations. The result of this is that there are empty spaces in the forming stations, which leads to deformations of the forming machine during the forming which are different from those in the fully loaded state. Such different deformations lead to fluctuations in the geometry of the acceptable parts produced. In addition, in hot-forming machines, different cooling of the tools and thermal shocks occur. All this can reduce the operating time of the forming machine up to the next tool change.
In the worse case, however, it is also conceivable that two end pieces (bar end and bar start following it) which are sticking together and are too short may certainly jointly have the desired length, but, pressed together, only apparently form a homogenous part. This error may possibly not be detectable and may then lead during operation to component failure, which is problematical in particular in the case of safety components, such as, for example, stub axles or steering parts.
In view of the disadvantages of the hitherto known shearing devices described above, the object of the invention is as follows: a forming machine having a shearing device for shearing a bar of the type mentioned at the beginning and a method of operating such a forming machine with which empty spaces in the forming stations can be avoided are to be provided.